Stress-oriented filament winding in composite panels

ABSTRACT

REMOVABLE TERRACED PERIPHERAL EDGES ON A ROTATING MANDREL ARE ADAPTED TO RECEIVE SUCCESSIVE WINDINGS OF THIN FILAMENT IN A PLURALITY OF SEPARATE LAYERES TO FORM REINFORCED COMPOSITE PANELS. THE MANDREL EDGES ARE REVERSED IN POSITION BETWEEN EACH WINDINGS STEP TO PERMIT WINDING OF FILAMENTD AT STRESS-ORIENTED CROSS-PLY ANGLES   WITH A MINIMUM OF FILAMENT WASTAGE, AFTER WHICH THE WORKPIECE COMPONENTS ARE DIFFUSION BONDED TOGETHER. RARE EARTH OXIDES ARE USED IN STOP-OFF COATING TO PREVENT BONDING OF WORKPIECE MATERIALS TO MANDREL SURFACES.

" Nw. 2, 1971 D. 1. SINFZER ETAL 3,616,822

STRESS-ORIENTED FILAMENT WINDING IN COMPOSITE PANELS Original Filed June16, 1967 2 Sheets-Sheet 1 INVENTOR Y Y O E T N T m R T E T BE A G DI LRR EE RUN N A a LGH Dwwm V U AA HO DDL m C n. I. SINIZER ETAL 3,616,822

STRESS-ORIENTED FILAMENT WINDING IN comrosrrm PANELS Original Filed June16, 1967 2 Sheets-Sheet 3 gg /r E .151zzzazzcqszzzzzqszziezeeza2:

I q z |4 555rra1$555552:szzezeflxfimemmfizzzmg- INVENTOR HQ 7 DAVID I.SINIZER, ALBERT TOY 0 s. ATTERIDGE S H. FANELLI ATTORNEY United StatesPatent 3,616,822 STRESS-ORIENTED FILAMENT WINDING IN COMPOSITE PANELSDavid I. Sinizer, Playa del Rey, Albert Toy, Gardena, David G.Atteridge, Santa Monica, and Louis H. Fanelli, Los Angeles, Calif.,assignors to North American Rockwell Corporation Original applicationJune 16, 1967, Ser. No. 646,582, now Patent No. 3,537,170, dated Nov. 3,1970. Divided and this application Feb. 9, 1970, Ser. No. 14,703

Int. Cl. B21f 3/04 U.S. Cl. 140-92.2 1 Claim ABSTRACT OF THE DISCLOSURERemovable terraced peripheral edges on a rotating mandrel are adapted toreceive successive windings of thin filament in a plurality of separatelayers to form reinforced composite panels. The mandrel edges arereversed in position between each winding step to permit winding offilaments at stress-oriented cross-ply angles with a minimum of filamentwastage, after which the workpiece components are diffusion bondedtogether. Rare earth oxides are used in stop-off coatings to preventbonding of workpiece materials to mandrel surfaces.

This is a division of application Ser. No. 646,582 filed June 16, 1967,now Pat. No. 3,537,170.

BACKGROUND OF THE INVENTION In the fabrication of composite filamentreinforced materials, filament winding techniques are known to the priorart whereby the composite is initially formed by rotating a mandrel toform filament layers. The directional strength properties of theresulting composites are vastly improved by orienting filament directionso as to achieve a cross-ply angle between the layers. Composites ofthis type which are easiest to manufacture utilize a cross-ply angle of90 between the dominant filament direction in two successive layers.

One of the problems sought to be solved by the concept in this caserelates to the manufacture of filament reinforced composite panelswherein the filaments are situated at cross-ply angles other than 90,and especially where cross-ply angles of any desired amount such as 22/2 between dominant directions of filament orientation may be achievedwith a minimum of filament or other workpiece material wastage.Extensive experience to date with filament reinforced structuresindicates that maximum efficiency and economy in the use of filamentmaterials, many of which are very expensive, costing as much as $5000per pound in the case of beryllium, conclusively demonstrates that thedirection of each successive filament layer should be oriented accordingto thedirection of external loads to be applied on the resulting finalstructure to achieve such efficiency.

In order to wind a multi-layer filament reinforced panel on a square orrectangular mandrel, such as segmented mandrel 100 shown in 'FIG. 5, themandrel with its segmented parts assembled in the relationship shown byFIG. may first be rotated about an axis of rotation 3-3 to form a firstlayer of parallel filaments which may contact each other and which willhave a direction substantially normal to axis 33, after which themandrel may be rotated about a second axis 4-4 shown in FIG. 6 while asecond layer of filaments is progressively wrapped about the mandrel andthe workpiece components assembled thereto. Between the foregoingwinding steps, corner portions 114, 116, 118 and 120 may be removed fromcenter portion 112 of segmented mandrel 100 and reassembled thereto inthe relationship shoWn Patented Nov. 2, 1971 by FIG. 6. After bonding ofthe assembled workpiece components to form panels having the same sizeand shape as center portion 112 of segmented mandrel 100, it may be seenthat the actual size of a rectangular workpiece having both plies offilament windings oriented in the desired directional relationship withrespect to each other coincides with the area enclosed by the solid linedesignated by reference numeral 5 in FIG. 7 and having cornersdesignated by numerals 6, 7, 8 and 9. As a result, the varioustriangular areas situated outside line 5 in FIG. 7 define portions ofworkpiece materials which will have to be removed and discarded,representing a useful yield in the final workpiece of about percent orless of the total workpiece materials and involving a considerableexpense in the manufacturing operation.

SUMMARY OF INVENTION According to a preferred embodiment of thisinvention, a substantially flat plate having parallel top and bottomsurfaces is provided for use as a mandrel in forming a plurality ofcomposite plates or panels of filament reinforced matrix. The novelmethod begins with placement of a sheet or film of stopoff material inclose and continuous surface area contact on either side of the mandrel.Thereafter, a sheet of matrix material which may illustratively comprisealuminum also generally having the same shape as the mandrel is placedin close continuous contact with the stopoff layer. The mandrel is thenrotated slowly about an axis While a single strand of filament isprogressively wound entirely around the mandrel and the matrix sheetssecured to either side thereof to form a layer of closely contacting andsubstantially parallel filaments. The wound filaments are securely heldin place by tape or adhesive proximate the edges thereof when necessary.Such tape is removed before the bonding step is undertaken. After eachfilament layer is completed, another layer of matrix material is placedin contact with the filament layer and the mandrel and workpiececomponents assembled therewith are again rotated about an axisdirectionally differing from the first mentioned rotation axis whileanother layer of filament is progressively wound from one end to theother of the entire mandrel and workpiece assembly. A final layer ofmatrix material is placed on either side of the assembled workpiececomponents and the entire assembly is subjected to heat and pressure insufficient amounts and for a period of time necessary to causesubstantially continuous bonding of the matrix and contacting filamentelements together. Thereafter, the mandrel is separated from theworkpiece components between which the mandrel is sandwiched, and twoseparate and identical workpiece composite sheets or panels areobtained. The fiber direction in eachpanel will be substantiallyperpendicular of the two different axes of rotation, whereby the angularorientation of the two stated axes with respect to the mandreldetermines the directional orientation of each respective fiber layer.Moreover, when using the novel mandrel shown in FIGS. l4 herein, each ofthe panels may be trimmed as necessary with a minimum of resulting lossin workpiece materials to obtain perfectly rectangular panels asindicated by lines 22, 24, 26 and 28 in FIG. 3.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a general perspective andfragmented view of a mandrel and workpiece assembly in a preparatorystage before bonding of the same according to the inventive methoddisclosed herein,

FIG. 2 shows a fragmented view, partly in cross section, taken alongline 2-2 in FIG. 1,

FIGS. 3 and 4 show plan views of the mandrel shown in FIG. 1, with theedge portions reversed in position on the mandrel,

FIGS. and 6 show a rectangular mandrel with edge portions of differentshape than that shown in FIGS. 1 through 4 and in alternate positions,

FIG. 7 shows the final part size compared with wound filament area inconnection with the apparatus of FIGS. 5 and 6,

FIG. 8 shows a cross-sectional view through a workpiece fabricated withthe apparatus of FIGS. 1-4 and taken along lines 88 in FIG. 3, and

FIG. 9 is an isolated fragmentary view of a detail modification of themandrel shown in FIG. 1.

DETAILED DESCRIPTION OF INVENTION Referring to FIGS. 3 and 4 it may beseen that the invention initially contemplates a mandrel 10 having aplate-like center portion 12 with substantially parallel top and bottomsurfaces, and a plurality of peripheral portions 14, 16, 18 and 20,removably secured to center portion 12 by suitable means such as aplurality of screws or bolts. Center portion .12 may illustratively beof quadrilateral shape as seen in FIGS. 3 and 4, comprising edges 22,24, 26 and 28 enclosing corner angles A, B, C and D. Edge portions 14,16, 18 and 20 of mandrel 10' are releasably held in continuous bearingcontact with edges 22, 24, 26 and 28, respectively, by theaforementioned bolts, three of which are designated by referencenumerals 30, 32 and 34 in FIG. 1.

For reasons which will appear more clearly below, the workpiece sheetsor slabs resulting from use of the ap paratus disclosed herein generallycorrespond in area with center portion 12 shown, for example, in FIG. 3.The finished workpiece will generally conform with that illustrativelyshown by FIG. 8, which shows a crosssectional view through a panelhaving separate layers 42, 44 and 46 of filaments embedded in a mass 48.Two identical panels are formed by each Winding step on mandrel 1 0, oneabove and one below the mandrel, as shown by FIG. 2, for example.

The novel process may begin with placement of a separating or stopofflayer of material overlying center portion 12 of the mandrel andfunctioning to prevent permanent joinder of workpiece materials to themandrel. The mentioned layer is shown in FIG. 1 and designated bynumeral '40, which may comprise a thin sheet of hard anodized aluminumwhen the workpiece materials comprise aluminum sheets, since an aluminumsurface will not diffusion bond with an anodized aluminum surface.Alternatively, the surface of mandrel 10, especially center portion 12thereof, may be coated with a material adapted to prevent bonding of theworkpiece components therewith during the bonding cycle. The coating isapplied directly to the clean surface of the mandrel such as by brushingthe material onto the surface or by dipping the mandrel into a slurry ofthe coating material followed by a curing step where necessary ordesirable. The stated coating material preferably comprises an aqueousslurry of calcium oxide which is chemically inert and non-reactive bothwith respect to stainless steel and to titanium, aluminum and many othermandrel or workpiece metals or alloys.

The finished workpiece which results from the process disclosed hereinmay be seen from FIG. 8 to comprise several individual layers 42, 44 and46 of elongate, substantially cylindrical wires, rods or filamentsembedded within a matrix or unitary mass generally designated byreference numeral 48 and consisting of layers '50, 52, 54 and 56 whichinitially comprise separate sheets and become integrally united by thediffusion bonding process to form matrix mass 48.

Illustratively assuming that the workpiece materials will comprise boronfilaments in a matrix of titanium, initial layup of the assemblyfollowing the preparatory steps mentioned above will begin by placementof the first matrix layer which is precut to coincide generally with thesize and shape of mandrel center portion 12, in substantially continuoussurface contact with center portion 12 or with stopoff sheet 40 whereused. After initial placement of matrix sheet 50, which may be securedin place by suitable means such as small pieces of masking tape at theedge or corner portions thereof, mandrel 10 with the mentioned sheetssecured thereto is mounted for rotation by suitable means (not shown)about an axis shown in FIG. 3. It will be understood that both the upperand the lower parallel surfaces of center section 12 are used to supporttooling and workpiece elements exact-1y corresponding with those shownin FIG. 1, for example, and discussed hereinbelow, whereby two identicalworkpieces result from the winding process disclosed herein. Winding offilament layer 42 is preferably accomplished by use of a reel ofcontinuous filament which is moved transversely relative to axis 60 at asubstantially constant rate while mandrel 10 rotates at a similarlyconstant rate, whereby the individual strands or filaments comprisinglayer 42 are progressively overlaid in contact with the preplaced sheets50 on each side of center portion 12. The filament direction of thecontinuous strand as it leaves the supply spool and approaches themandrel should define substantially a 90 angle with axis 60.Alternatively, the mandrel may be fixed while a carrier with multiplespools moves around the stationary mandrel.

Winding may appropriately begin at corner B as seen in FIG. 3, wherebythe individual filament will be wound between two surfaces 62 and 64formed on edge portions 14 and :16, respectively. Surfaces 62 and 64 maybe planar as suggested by FIG. 1, but are preferably semicylindricalabout center axes such as axis 67 which are substantially parallel toaxis 60, hence are adapted to receive each of the successive and closelyadjacent loops of filament as the same is wound entirely around edgeportions 14 and 16 together with center portion 12. As suggested by FIG.9, semi-cylindrical surfaces 63 and 65 have a diameter essentially equalto the thickness of mandrel center portion 12. If surfaces 62 and 64, orthe center axes thereof, were not substantially parallel with axis 60,lateral slippage of individual loops across one or both surfaces couldresult during winding operations. When the mentioned loops have entirelytraversed surfaces 62 and 64, which are of substantially correspondinglength, width and area, the same continuous strand will gradually passtoward the left as seen in FIG. 3 beyond transition surfaces 66 and 68and then begin a separate series of windings between surfaces 70 and 72.Thereafter, the process is repeated until the spool or other supplysource for the single continuous filament traverses the entire length ofaxis 66' until corner D is completely covered by filament layer 42.Alternatively, each step can be wound simultaneously with all theremaining steps with a separate spool for each step. Followingcompletion of the first winding step described above, filament layer 42is secured in place by suitable means such as small pieces of maskingtape or else by light application of adhesive or by flame spraying theend portions thereof proximate edges 22, 24, 26 and 28. With layer 42thus held in place, the outermost ends of the individual filamentstrands are cut or broken as indicated by reference numeral 74 in FIG.1, after which edge portions '14, 1,6, 18 and 20 are entirely removedfrom mandrel center portion 12.

Following removal of edge portions 14, 16, 18 and 20 as discussed above,the stated edge portions are reversed in position and remounted oncenter portion 12 of mandrel 10 as shown, for example, by FIG. 4. Thus,surface 62 shown in FIG. 4, is proximate corner A rather than in theposition shown by FIG. 3 where surface 62 was proximate corner B.Similarly, the remaining edge portions of mandrel 10 are reversed inFIG. 4 compared with the positions for each edge portion shown in FIG.3. As a result of the stated reversal, it may be seen that filamentlayer 44 applied over second matrix sheet 52 shown in FIG. 1 may beaccomplished about an axis 76 whereby progressive movement of the supplyroll along a path parallel with axis 76 and beginning proximate corner Awill result in a plurality of separate loops extending around mandrelbetween surfaces 62 and 64 shown in FIG. 4. At the completion of windingabout axis of rotation 76, the process is repeated, whereby anothermatrix layer 54 is placed over layer 44, the windings are temporarilysecured in place by tape or by flame spraying, edge portions 14, 16, 18and 20 are removed and reversed in position on center portion 12. ofmandrel 10, and the assembled mandrel and workpiece components are againrotated about axis 60 to form another filament layer 46. The statedwinding steps may be repeated any desired number of times to produce anydesired number of filament layers in the finished panels.

The final step after all filament winding has been completed isplacement of a matrix sheet over the last filament layer on either sideof mandrel 10, such as layer 56 in FIG. 1, after which the tapes orother temporary holding means are removed and the workpiece and mandrelassembly, preferably without edge portions 14, 16, 18, and 20, is placedin an airtight container such as a steel retort 80-. Thereafter, theretort is welded or otherwise closed completely to hold the matrixsheets and filament layers in close surface contact and to isolate thecontents of the retort from surrounding atmosphere. The retort ispreferably evacuated or else filled with a suitable inert gas such asargon or helium, after which the diffusion bonding of filament andmatrix layers to form substantially unitary mass 48 shown in FIG. 8 isaccomplished by subjecting retort 80 and its contents to sufficient heatand pressure to effect solid-state joinder of the workpiece materialsaccording to principles known heretofore, the details of which are notgermane to the invention in this case. Following completion of diffusionbonding, the workpiece assembly is removed from retort 80 and the twoduplicate panels are separated from each side of mandrel center portion12.

The prior art involving solid-state or intermolecular diffusion bondingincludes issued U.S. Pats. 3,145,466; 3,180,- 022; 3,044,160; 2,850,708;and 3,170,234. The precise values of time, temperature and pressureutilized in connection with bonding of workpiece materials is not acritical or limiting feature of the broad concept disclosed herein, andspecific materials 'with which the concept is usable are stated forillustration only. The method disclosed herein has been usedsuccessfully with matrix materials of aluminum, copper, nickel, andtitanium; and filament materials of boron, beryllium, tungsten, siliconcarbide and stainless steel. The number of filament layers has beenvaried over a wide range in different workpieces, from two to forty,with a commensurately wide range of panel thicknesses and filamentdensities.

As noted hereinabove, FIGS. 5 and 6 show alternative embodiments of theinventive concept disclosed herein, but are not preferred because of thehigher proportion of workpiece material losses for each finishedcomposite panel compared with the embodiment shown in FIGS. 1-4.However, some advantages are obtained from the approach disclosed inFIGS. 5 and 6 compared with fabrication techniques known to the priorart, such as adaptability of the winding process for use with standardlathes. Thus, the mandrel can be turned between centers on a lathe,while wire filament is fed from a spool laterally moved by the lathetool mount so that filament spacing is controlled by adjusting the lathefeed rate.

While the stopolf coating of calcium oxide mentioned hereinabove iseffective in preventing diffusion bonding of workpiece materials withmandrel surfaces, it is basic to the inventive concept disclosed hereinthat oxides of rare earth elements are useful as stopoff materialsinstead of CaO because they are chemically more stable than the oxidesof most matrix materials such as titanium and aluminum. It has beenfound, for example, that yttrium oxide (Y O is superior to calcium oxidein some cases, notably where matrix sheet 50 is of titanium. Also, it isespecially helpful in the application of the stopoff coating if suchcoating is in a thickened semi-liqud or paste-like state which willadhere to some extent on the surface to which it is applied. Calciumoxide will adhere when combined with water in an amount sufficient toproduce a paste-like consistency without requiring addition of a binder.Although yttrium oxide will adhere to a metallic surface sufficientlyfor some applications, it has been found that the addition of a binderthereto facilitates handling procedures during initial layup of theworkpiece assembly by rendering the stopoff coating tougher and moreresistant to removal through jarring or through direct contact. The bestagent for providing the stated function is 3% by weight of a potassiumsilicate solution commercially known as Kasil #6 made by PhiladelphiaQuartz Company. In addition, a stopoff compound of cerium sulfide (CeS)gives good results with or without a binder such as described above, butis less practical than those already mentioned due to the relativelyhigh cost of cerium sulfide. Gadolinium and samarium are furtherexamples of rare earth materials, the oxides of which are useful instopoff compounds.

While the particular details set forth above and in the drawings arefully capable of attaining the objects and providing the advantagesherein stated, the specific materials and method thus disclosed aremerely illustrative and could be varied to produce the same resultswithout departing from the scope of the inventive concept as defined inthe appended claim.

We claim:

1. A method of forming a multi-layer filament reinforced panel having aplurality of separate layers of filaments, each of said layers having across-ply angle of filament direction relative to the next nearest layerof filaments, said method comprising:

supplying a continuous single strand of said filament to a segmentedplate-like mandrel having two substantially parallel surface areas,

rotating said mandrel about a first rotation axis substantially parallelto and midway between said surface areas,

said mandrel comprising a rectangular center portion and a plurality ofremovable edge portions secured to said center portion and each havingat least one surface substantially parallel to said first axis of saidrotation,

moving said single strand along a first linear path substantiallyparallel and spaced apart from said first rotation axis so that saidfilament is wound about said mandrel progressively forming a firstfilament layer thereon,

holding said first filament layer on said mandrel while removing saidremovable edge portions from said center portion and replacing said edgeportions on said center portion with said one surface in a differentposition than that identified with said first filament layer, and

supplying said strand to said rotating mandrel while moving said strandalong a second linear path substantially parallel to a second rotationaxis midway between said surface areas to progressively form a secondfilament layer about said mandrel,

said second axis being angularly displaced from said first axis.

References Cited UNITED STATES PATENTS 3,303,010 2/1967 Copenheferl4092.2

LOWELL A. LARSON, Primary Examiner US. Cl. X.R.

